1. Technical Field
The disclosure relates generally to angel wing seals for turbomachines, and more particularly, to a turbomachine bucket having an angel wing configure to seal with a number of different sized discouragers and related methods.
2. Background Art
The typical design of most turbomachines is known in the art. They include a compressor for compressing air that is mixed with fuel. The fuel-air mixture is ignited in an attached combustor, to generate combustion gases. The hot, pressurized gases are allowed to expand through a turbine nozzle, which directs the flow to turn an attached, high-pressure turbine. The turbine is usually coupled with a rotor shaft, to drive the compressor. The core gases then exit the high pressure turbine, providing energy downstream. The energy is in the form of additional rotational energy extracted by attached, lower pressure turbine stages, and/or in the form of thrust through an exhaust nozzle.
In the typical scenario, thermal energy produced within the combustor is converted into mechanical energy within the turbine, by impinging the hot combustion gases onto one or more bladed rotor assemblies. The rotor assembly usually includes at least one row of circumferentially-spaced rotor blades. Each rotor blade includes an airfoil that includes a pressure side and a suction side. Each airfoil extends radially outward from a rotor blade platform. Each rotor blade also includes a dovetail that extends radially inward from a shank extending between the platform and the dovetail. The dovetail is used to mount the rotor blade within the rotor assembly to a rotor disk or spool.
The rotor forms part of a stator-rotor assembly. The rows of rotor blades on the rotor assembly and the rows of stator vanes on the stator assembly extend alternately across an axially oriented flowpath for ‘working’ the combustion gases. The jets of hot combustion gas leaving the vanes of the stator element act upon the turbine blades, and cause the turbine wheel to rotate. The element which remains stationary while the turbine rotates at high speed can also be referred to in the art as the nozzle or diaphragm of a turbomachine frame.
An opening at the interface between the stator element and the blades or buckets can allow hot core gas to exit the hot gas path and enter the wheel-space of the turbomachine. In order to limit this leakage of hot gas, the blade structure typically includes axially projecting angel wing seals, also simply referred to as angel wings. According to a typical design, the angel wings cooperate with projecting segments or ‘discouragers’ which extend from the adjacent stator element, i.e., the nozzle. The angel wings and the discouragers overlap (or nearly overlap), but do not touch each other, thus restricting gas flow.
A gap remains at the interface between adjacent regions of the nozzle and turbine blade, e.g., between the adjacent angel wing-discourager projections, when such a seal is used. The presence of the gap, i.e., clearance, is necessary at the junction of stationary and rotating components to allow for the rotation. However, the gap provides a path which can allow hot core gas to exit the hot gas path into the wheel-space area of the turbomachine. The leakage of hot gas by this pathway is disadvantageous for a number of reasons. First, the loss of hot gas from the working gas stream causes a resultant loss in energy available from the turbomachine. Second, ingestion of the hot gas into turbine wheel-spaces and other cavities can damage components which are not designed for extended exposure to such temperatures, such as the nozzle structure support and the rotor wheel.
Conventionally most turbomachine blades or buckets, such as those used in gas turbines, are designed for a particular sized discourager of a corresponding turbomachine frame and are not interchangeable for buckets designed for a differently sized discourager due to the different geometries of the frames. For example, FIG. 1 shows two conventional buckets having respective angel wings 2, 4 interposed with two different sized discouragers 6, 8. As illustrated, the two buckets are not interchangeable because of the different angel wings and discouragers. As noted above, different interference fits and/or undesirable cooling performance may be created when an improperly sized bucket is used. For example, where angel wing 2 is used with discourager 6, no overlap would exist; similarly, where angel wing 4 is used with discourage 8, too much overlap may exist. Consequently, new or additional castings must be manufactured in order to generate specific blades or buckets with specifically sized angel wings 2, 4 to be installed in different frames having different sized discouragers 6, 8 to perform with the same design intent.